Matt McClain/ The Washington Post via Getty Images(WASHINGTON) -- A memorial service was held on parade grounds at the Marine Barracks Sunday evening to honor the victims of Monday's Navy Yard shooting.

The ceremony honored the 12 people who lost their lives just blocks away in the mass shooting spree. More than 4,000 people were in attendance Sunday to mourn.

With the flag flying at half staff, President Obama spoke at the memorial. "We cannot begin to comprehend your loss," Obama said to the families of the victims.

"The tragedy and the pain that brings us here today is extraordinary. It is unique. The lives that were taken from us were unique. The memories their loved ones carry are unique and they will carry them and endure long after the news cameras are gone," Obama said.

He also referenced the pattern of mass violence in the country. "As President, I have now grieved with five American communities ripped apart by mass violence. Fort Hood, Tucson, Aurora, Sandy Hook, and now the Washington Navy Yard."

The murder rate in America is three times more than in other developed nations, and gun violence in America is 10 times more than in other developed nations, Obama said.

"There is nothing normal" about these tragedies, Obama said.

"Once more our hearts are broken," Obama said. "Once more we ask why."

Other speakers included Washington D.C. Mayor Vincent Gray, Secretary of the Navy Ray Mabus, and Secretary of Defense Charles Hagel.